In 1981 when GM redesigned the Chevy/Gmc trucks one of the few changes was to the body mounts to make them more flexible.
In changing them GM also went from a seperate 2 and 4 wheel drive body mount style to a simpler mount that was used on both C and K series trucks (and R & V series 88-91 trucks after the complete redesign for the 88 body style)
I scanned one of my catalog pages and added a couple things for reference.